warning: cast between incompatible function types from FARPROC_ to gettickcount64_t

[kivadiu]

While building 1.68.0 beta 1 on x86_64 cross-compiling to Windows 32 bits with mingw-w64 + g++ 8.2.0, I get the following warning:

"i686-w64-mingw32-g++-8.2.0"   -I/softs/win32-mingw-8.2.0/release/iconv/include -I/softs/win32-mingw-8.2.0/release/gettext/include -I/softs/win32-mingw-8.2.0/release/bzip2/include -I/softs/win32-mingw-8.2.0/release/zlib/include -I/softs/win32-mingw-8.2.0/release/jpeg-turbo/include -I/softs/win32-mingw-8.2.0/release/xz/include -I/softs/win32-mingw-8.2.0/release/tiff/include -I/softs/win32-mingw-8.2.0/release/png/include -std=c++14 -O2 -DNDEBUG -m32 -mthreads -O3 -finline-functions -Wno-inline -Wall -pedantic -march=i686 -Wextra -Wno-long-long -Wno-unused-parameter -Wunused-function -pedantic -DBOOST_ALL_NO_LIB=1 -DBOOST_ASIO_NO_DEPRECATED -DBOOST_CHRONO_STATIC_LINK=1 -DBOOST_FILESYSTEM_NO_DEPRECATED -DBOOST_LOG_WITHOUT_EVENT_LOG -DBOOST_SYSTEM_NO_DEPRECATED -DBOOST_SYSTEM_STATIC_LINK=1 -DBOOST_THREAD_BUILD_LIB=1 -DBOOST_THREAD_USES_CHRONO -DBOOST_THREAD_WIN32 -DBOOST_USE_WINDOWS_H -DNDEBUG -DWIN32_LEAN_AND_MEAN  -I"." -c -o "bin.v2/libs/thread/build/gcc-8.2.0/release/link-static/target-os-windows/threadapi-win32/threading-multi/win32/thread_primitives.o" "libs/thread/src/win32/thread_primitives.cpp"
libs/thread/src/win32/thread_primitives.cpp: In function 'boost::detail::win32::ticks_type boost::detail::win32::{anonymous}::get_tick_count_init()':
libs/thread/src/win32/thread_primitives.cpp:97:120: warning: cast between incompatible function types from 'boost::winapi::FARPROC_' {aka 'int (__attribute__((stdcall)) *)()'} to 'boost::detail::win32::detail::gettickcount64_t' {aka 'long long unsigned int (__attribute__((stdcall)) *)()'} [-Wcast-function-type]
             (boost::detail::win32::detail::gettickcount64_t)boost::winapi::get_proc_address(hKernel32, "GetTickCount64");
                                                                                                                        ^

[viboes]

Hi, thanks for reporting this.

It seems there is yet an issue when we moved to winapi. @Lastique, do you have any idea of c-what can be done?

[Lastique]

The only thing I can suggest is to silence or work around the warning. The code is correct, AFAICS, this is the intended usage pattern of GetProcAddress, which indeed requires a cast between potentially different types of function pointers.

[viboes]

It is weird to cast between "potentially different types of function pointers", isn't it? What could be the expected result of such a kind of casts?

[Lastique]

Not so weird, not really. GetProcAddress returns a pointer to some function. It can return pointers to different functions, so it has to return something that is suitable to store any pointer to function. Microsoft chose FARPROC, which is int (WINAPI *)() on 32-bit Windows. The user is supposed to know the signature of the function he requests and perform a cast (which is a nop on this platform). The result is a pointer to function with the required signature, which is bitwise equal to what GetProcAddress returned.

This may not be a well defined standard C++, but, well, that's now 95% of system programming works.

[kivadiu]

So it's really harmless. I'm happy to hear that.

[viboes]

Ok, I would accept a PR that silent this warning.

Sorry, I don't have a Windows platform to test it.

[kivadiu]

Any idea why PR #227 failed some tests in appveyor? It seems completely unrelated to my patch.

[viboes]

See #227